This invention relates to an apparatus to control of the flow rates of fluids. It is particularly concerned to provide a means whereby the flow rates of two or more fluids to be mixed are controlled and is especially intended for use in the mixing of the components of a post-mix beverage.
In the dispensing of a post-mix beverage, i.e. in which the components of the beverage are mixed at the point of sale from one or more fluid components, e.g. a concentrated syrup and a diluent, usually plain or carbonated water, it is obviously desirable to provide a mixed beverage of the correct ratio of components and it is important that this ratio should not vary beyond tightly controlled limits. It is, therefore, desirable to have some means of determining the amount of each component being provided to, for example, a dispense nozzle. One way of achieving this is to determine the flow rate of each component, either by direct measurement or by calculation after measurement of another property, and to calculate the amount dispensed from a series of flow rate determinations with respect to elapsed time.
It is an object of the present invention to provide an improved means of accurately mixing fluids, particularly beverage fluid components, in a desired ratio. It is also an objet of the present invention to provide an improved means of determining fluid flow rate values.
Accordingly the invention herein provides an apparatus for the mixing of at least two fluids, which comprises a first fluid supply line connectable to a source of the first fluid, a second fluid supply line connectable to a source of the second fluid. The invention also includes a mixing head into which the two fluids can be supplied through their respective supply lines and mixed therein and dispensed there from. The first fluid supply line passes through an orifice in an orifice plate and a pressure transducer is positioned to measure the pressure drop in the fluid passing through the plate. The pressure transducer provides the measured pressure data to a controller, the controller being pre-programmed with flow rate values determined over a range of pressure drops for the first fluid and to control the rate of flow of the second fluid to the mixing head in response to the flow rate of the first fluid to achieve a desired flow ratio of the two fluids. The controller may allow flow for a predetermined time dependent on the monitored flow rates in order to achieve a specific volume of dispensed fluids.
As indicated above, the invention is particularly intended for use in the dispensing of post-mix beverages and will, therefore, be more particularly described below with particular reference to that embodiment. The mixing head may conveniently include a dispense nozzle from which the mixed beverage maybe dispensed into a suitable receptacle. The first fluid is preferably a concentrated syrup and the second fluid is preferably a diluent, e.g. plain or carbonated water. The second fluid supply line may contain any suitable flow rate measuring device e.g. a flow turbine, and this is flow rate sensor is also connected to the controller. Thus, the flow rate of the second fluid/diluent may also be monitored in addition to the pressure transducer monitoring of the first fluid/syrup. The controller is also connected to a valve in the second fluid supply line and can cause that valve to be opened to the desired amount to achieve the required flow rate for the dispense ratio for the particular beverage being dispensed.
By monitoring the second fluid rate in conjunction with that of the first fluid rate and, where necessary, adjusting the second fluid flow rate to correspond to any variations in the monitored first fluid flow rate, the ratio of the dispensed beverage can be accurately maintained at the required value. Thus any variations in the flow rate of the concentrate of a post-mix beverage, e.g. due to pressure variations in the supply line or delays in response of the on/off valve through which the concentrate is supplied, can be monitored and taken into account by rapid consequential adjustments to the diluent flow rate.
The concentrate supply line may contain a simple on/off valve to allow the concentrate to flow when a beverage dispense is signalled to the controller. The controller then causes the valve, e.g. a solenoid or diaphragm valve, to open while at the same time, or fractionally earlier, opening the on/off valve in the diluent supply line and commencing monitoring of the two flow rates. In this embodiment, therefore, the concentrate valve is either open or closed and when open it remains fully open to provide a particular nominal flow rate. The valve may have, e.g., a manual adjuster to fine tune this nominal flow rate for particular concentrates. The pressure transducer in this embodiment is essentially, therefore, providing monitoring of flow rate fluctuations above and below the nominal rate through the fully opened valve.
In another embodiment, the on/off valve in the concentrate flow line may be controllable to provide a range of flow rates of the concentrate whereby the controller maybe programmed to control dispense of a wider range of beverages based on a greater number of different concentrates that may be supplied one at a time through the first fluid supply line. In a particular preferred version of this latter embodiment, the valve in the concentrate supply line is of the type described and claimed in our international patent publication WO99/29619 (application no. PCT/GB98/03564). That international application describes and claims a valve comprising a substantially rigid housing containing a passageway between an inlet and an outlet of the valve, a closure member movable in the passageway from a first position in which the valve is fully closed to a second position in which the valve is fully open, the closure member engaging the wall of the passageway to seal the passageway, the wall of the passageway or the closure member defining at least one groove, the groove having a transverse cross-section that increases in area in the downstream or upstream direction, whereby movement of the closure member from the first position towards the second position opens a flow channel through the groove. The groove(s) may be, for example, of tapering V-shape and will, for convenience, hereafter be referred to as xe2x80x9cV-groovesxe2x80x9d and the valves of this general type as xe2x80x9cV-groove valvesxe2x80x9d, although it will be appreciated that the grooves may, if desired, have a different tapering cross-section, e.g. of circular, rectangular or other shape.
The progressive increase or decrease in area of the groove flow channels can produce excellent linear flow through these V-groove valves, i.e. for a given pressure the flow rate is more directly proportional to the valve position than for conventional valves. This enables better control of the flow rate over the entire operating range of the valve. Alternatively the V-groove valve may be replaced, for example, by a solenoid, on/off valve upstream of a needle valve to provide the desired range of concentrate flow rates. The means to open and close the adjustable concentrate valve may be any suitable mechanism. A stepper motor or a linear solenoid actuator are amongst the preferred mechanisms.
The valve to control the flow of diluent may also be, if desired, a V-groove valve. Pressure transducers are well known in the art and the skilled man will readily be able to choose one suitable for his particular needs. Essentially, the pressure transducer measures fluid pressure at a particular point or surface and converts this measurement into an electrical signal. The electrical signal is fed to the control means which, therefore, is programmed to receive the pressure data in this electrical form.
The orifice plate may be positioned upstream or downstream of the on/off valve in the concentrate supply line but it is preferred that it be upstream as this arrangement, although possibly subject to static pressure variations, is less likely to be affected by variations in flow characteristics through the orifice plate. Nevertheless, it may be desirable in certain circumstances to position the orifice plate downstream of the on/off valve and, in one such embodiment, the orifice plate may be positioned immediately before the outlet of the concentrate supply line to the mixing head. In this arrangement the plate can vent to atmosphere and the pressure transducer measures the pressure immediately upstream of the plate. However, it is preferred to measure the pressure difference across the orifice in the plate and this may be done whether the plate is positioned upstream or downstream of the on/off valve. Preferably, the positioning of the orifice plate, when not venting to a atmosphere as described above, in the supply line should be such that the supply line at the downstream side of the plate remains full of the concentrate. Thus the flow line through the plate should preferably be uphill or at least horizontal. By this means there is less likelihood of trapped air affecting the pressure measurements and hence the flow rate values.
It will be appreciated that fluid flow characteristics through the orifice plate are affected inter alia by the size of the orifice, the sharpness of the edge leading into the orifice and the thickness of the plate. In principle, the thinner the plate the better in that the fluid can then effectively be considered to be passing through a very short tube. The shorter the tube the less xe2x80x9cre-attachmentxe2x80x9d effect of the fluid to the wall of the tube and the less undesirable effect on the flow and the flow rate measurement. Clearly too thin a plate may buckle under the fluid pressure and we have, therefore, found, that as an alternative to a very sharp orifice edge on a slightly thicker plate, which edge maybe expensive to manufacture, a chamfered edge leading into or leading out of the orifice may be usefully employed to give a predictable characteristic at the cost of slight increase in viscosity sensitivity.
Where the concentrate valve is adjustable to provide a range of concentrate flow rates, the controller may be programmed to provide a xe2x80x9cprofiledxe2x80x9d dispense for the beverage. In other words, the initial portion of the dispense may, for example, be at a low flow rate, e.g. to prevent initial over-foaming of a carbonate beverage, and then the rate may be increased to fall for the majority of the dispense period and then reduced to a slower rate again for the final filling of the glass or other receptacle. Thus the dispense pour may be controlled to suit the particular beverage in question.
As indicated above, the controller may be programmed to dispense a number of different beverages. It may also be programmed to dispense different volumes, e.g. a small portion and a large portion, of each beverage. The controller may also be programmed to take into account viscosity changes due to temperature variations. This can be achieved by the appropriate positioning of a temperature sensor in one or each fluid supply lines so that the correct ratios of fluids can be maintained regardless of temperature variations.